Uranium metal and product and process of making the same



Patented May 20, 1930 UNITED STATES PATENT or'r cs JOHN ALLEN HEANY, onNEW HAVEN, connncrrcu'r, assxenoa; Bx MESNE ASSIGN- mrs, 'ro ABGTU'BUSname TUBE company, or NEWARK, NEW JERSEY, A coa- POBATION OF DELAWARE'UIB-AIITUI METAL AND PRODUCT AND PROCESS OF MAKING- THE SAME .loDrawing.

This invention relates to uranium metal alloys and the process formaking the same. More specifically, the invention relates to uraniumalloys suitable for use in thermionic tubes for radio reception or X-rayproduction.

Generally stated, the invention consists in a process of manufacturing ametal materlal,

the essential part of which is the element uranium. The uraniumgenerally appears in the completed material as an alloy or as a veryintimate mixtureof the metal with a refractory reinforcing element. Theinvention also involves the utilization of the material 1 as an electronemitting body for radio tubes, X-ray tubes, and the like.

Having consideration for the uses to which the newmetal may be applied,such as filaments for radio tubes, it is of interest to note thatheretofore either the metal tungsten or tungsten combined in a suitablemanner with thorium has been used to give the necessary electronemission for detection and amplification in radio reception. Thedisadvantage in the'use of tungsten has. been the necessity for arelativelyhigh-temperature in order to get the proper volume of electronemission.

The employment of the metal thorium as an alloy or mixture with tungstenor a coating of thorium oxide on the surface of tungsten filament hasresulted in an electron emission of considerably higher value for thetemperature used, and filaments of this type have largely replacedfilaments of pure tungsten.

One of the objects of the present invention is to provide a filamentarybody which may be used for radio tubes, for example, which has a higherrate of electron emission for a given temperature not only than puretungsten, but

40 also than that from the thoriated filaments.

Another important object is to provide a filament ofhigh electronemission which possesses also a high melting point, so that danger ofburning out in the process of manu- 5 facture and in use is largelyeliminated, and

Application filed October 22, 1925. Serial No. 64,255.

so that further the filament may be operated at any temperature at whichit gives maximum efliciency. Other objects relate to the Iprovision ofmeans for providing a highly efc1ent detector and amplifying tube forradio receiving apparatus; the provision of an uranium alloy which isductile so that it may be readily drawn to any desired size; theprovision of an alloy which may be readily worked into sheet or tubeform for use in a thermionic tube or as an externally heated ionizer;and other objects such as will appear on consideration of the followingdescription of one method of producing the alloy.

A method of manufacturing the alloy which I have found satisfactory forthe production of filaments for radio tubes will now be described, inwhich I employ molybdenum metal alloyed with uranium. Finely dividedmolybdenum metal is mixed with uranium oxide in such proportion ,as toproduce approximately 2% by weight of the total mixture of uranium metalafter reduction of the oxide. For example, to make a finished slugsuitable for swaging and wire drawing eight inches long andnine-thirty-second inches square, I take about 56 grams of molybdenummetal and about 1 grams of uranium oxide. This mixture is placed in ajar or ball mill and thoroughly mixed by this mechanical 75 method for aperiod varying from one to several hours. This mixture is then pressedinto slug form by means of a hydraulic press in which a veryconsiderable and heavy pressure is employed. Should the percentage ofingredients and the pressure permit, the slug may be placed at once inthe electric furnace for reduction, but where there is some fragility inthe slug, I may. sinter the same at a bright red temperature and in ahydrogen at mosphereprior to the reducing operation.

With the slug properlycompacted and suf- I ficiently strong to permithandling, I insert the same in an electric furnace which usually takesthe form of a chamber having electric period of 10 minutes, and in asubsequent period of 10 minutesthe amperage is increased from 300amperes to 1150 amperes. In a further period of 10 minutes, the amperageis held approximately constant at 1150 amperes and thereafter for aperiod of 2 minutes, the current is gradually reduced to zero.temperatures involved in this heating may vary from room temperatures toa point ap- -proximately equal to the temperature 010- tained at 92% ofthe current required to cause fusion or melting of the slug; that is, toa point sufliciently high to cause reduction of the uranium oxide. Theresult of the process is a mixture or alloy of molybdenum wlth uranium,the mass being welded or fused together in one solid metallic unit which1s capable of being mechanically worked.

Subsequent to the reduction process, the slug is swaged by one of theusual hot swaging processes, The usual method employed is to heat theslug in an electric furnace consisting of a tube of alundum or porcelainsurrounded by a heating coil and a heat insulating cover of magnesite,silica or other suitable material held by a suitable shell of asbestos.fibre brick. sheet iron, or the like. An inert gas, such as hydrogen, ispassed through the furnace and the slug is alternate- 1y heated in thisfurnace and forced through the dies of a swaging machine, thus bringingabout a gradual .reduction in the diameter of the material until finewire filamentary elements are obtained. Heating and swaging employed inthe treatment of the prepared slug will vary in accordance with therequirements of the .specific mixture employed.

The process as above described is limited to the mixture of molybdenumand the uranium oxide. Obviously, a similar process may be employed.where' tungsten or oxides other than uranium, or where other compoundsof uranium, are used. Also, I have found that the percentage of uraniumin the alloy to produce a material satisfactoryfor thermionic tubes, isnot critical, but values varying from 2 to 10% give very good results.

Where an alloy made of molybdenum and uranium is employed for thefilaments of radio tubes, exceptionally good results are obtainedinasmuch as the high electron emission of alloys and compoundscontaining The necessities of a high vacuum for radio tubes makes theuse of this alloy exceedingly advantageous, inasmuch as the addition ofmo lybdenum as the principal constituent partv of the alloy with itsrelatively high melting point temperature makes possible the hightemperatures necessary for flashing, bombarding and other processesincident to the construction of radio tubes. Moreover, the high meltingpoint of molybdenum is a safe guard against destruction of the filamentduring use, arising from accidental impression on the filament circuitof an over-voltage.

Another important advantage in the use of molybdenum with uranium isthat molybdenum is a highly ductile metal and is capable of easyadaptation to manufacturingprom esses, such as the formation of smallcoils of wire of exceedingly small diameter.

While I have described the invention as applied particularly to use inradio tubes, it is possibly of valuable use in X-ray tubes and otherdevices wherein a high electron emission is desired. The relativelyhigher emissive properties of uranium over thorium, for example inconjunction with the relatively higheruranium weight serves to make thealloy metal exceedingly advantageous for such uses, especially wherecombined with a refractory supporting metal which will permit usualmanufacturing operation without diminishing the value of the propertiesof the uranium metal itself.

Moreover, while I have described the process and product as pertainingspecifically to the alloy, it is apparent that by a constant repetitionof the reducing step with added quantities of the oxide, approximatelypure uranium may be produced which may be used as filaments for radiotubes and similar uses. Such filaments may be of pure urani-' um or oftungsten or molybdenum coated with uranium.

Modifications and uses of the invention other than those specified, maybe made by those skilled in the art, but the disclosure should beunderstood as illustrative rather than definitive, as indicated in theclaims hereunto appended.

Having thus described my invention, what I claim is: I 1. An alloy ofuranium and molybdenum, theuranium not exceeding 5% of the constituentsof the alloy.

2. A material having high electron emissivity, said material beingformed of an alloy of molybdenum and uranium, the uranium formingapproximately 3% of the alloy.

3. The process of making an alloy of ura'nium and another metal, whichconsists in mixing the uranium in the form of an oxide with theconstituent alloy metal, both substances o cooling said heated slug, theheating bein in powdered form; pressing the mixture 1n the form of asolid slug adapted to be positioned between the electrodes of anelectric power source; heating the slug from room temperatures to atemperature suflicient to cause reduction of the oxide during a timeinterval approximating 20 minutes; holding said maximum temperature fora period a proximating 10 minutes; and subsequent y of the slug takingplace in an atmosphere 0 hydro:

en. In testimony whereof, I aflix my signature.

JOHN ALLEN HEANY.

